Why has a portion of the Christian Community lost one of the psalms? Especially when the preceding psalm is used to promote such a critical concept within their faith?

The concept of Total Depravity is critical for much of Protestants theology. By believing all people are born with a complete lack of desire and interest and ability to follow God, Protestants argue that all of our (Catholic) religious practices, sacraments, celebrations, etc., are useless. Only those who are seen to have faith in Christ (meaning exactly the same view of the Christian faith as they have) form a small group of people who have been 'elected' for saving grace from the beginning of time by a sovereign God.

The key verse used by most Protestants to defend the idea of Total Depravity is found in the Book of Romans, 3:10-12.

As it is written:

“There is no one righteous, not even one; there is no one who understands; there is no one who seeks God. All have turned away, they have together become worthless; there is no one who does good, not even one.” NIV, from Bible Gateway

The question I ask is this:

If Paul quoted this verse from Psalm 14 of the Old Testament, which almost all Christians assert, then why are we trying to determine universal doctrinal truths from what is essentially a song?

Songs (Psalms) were no different in biblical times than they are today. Songs very often emphasize, exaggerate and paint lyrical pictures which engage the emotions of the listener. How often do we hear a song where a man claims a certain woman is the 'most beautiful woman in the world'? Do we really think that we should assume that whoever wrote the song actually believes that this particular woman is actually the absolute most beautiful woman out of the 3.5 billion women in the world? Can we take it as proven fact that she actually is the most beautiful simply because it is told to us within a line of a song?

That said, if we are in fact to take Psalm 14 to prove that every single human being ever born is 'Totally Depraved', that how do Protestants explain what we read in the very next Psalm? For within (the missing) Psalm 15 we read this.

Lord, who may dwell in your sacred tent? Who may live on your holy mountain?

The one whose walk is blameless, who does what is righteous, who speaks the truth from their heart; whose tongue utters no slander, who does no wrong to a neighbor, and casts no slur on others; who despises a vile person but honors those who fear the Lord; who keeps an oath even when it hurts, and does not change their mind; who lends money to the poor without interest; who does not accept a bribe against the innocent.

Whoever does these things will never be shaken.

No one can deny that Psalm 15 teaches us we can 'dwell' with God if they chose to live in the ways described. The one who 'does what is righteous'.

The Catholic faith does not promote an all-or-nothing approach to every aspect of our faith. We can explain and live with what we read in both for Psalm 14 and Psalm 15. Psalm 14 is not telling us we are entirely depraved. Psalm 15 is not telling us anyone can be entirely righteous beyond the need for a Savior. In other words, we realize all people are called by God to actually chose to act righteously and cooperate with his will and the graces he provides.